Photographic or cinematographic high-speed tele-objective



0R 2.972.2 55 M f 5;

Feb. 21, 1961 R. SOLISCH 2,972,285

PHOTOGRAPHIC 0R CINEMATOGRAPHIC HIGH-SPEED TEE-OBJECTIVE Filed Nov. 13, 1958 I In mvmron: Puda/f 604/509 M Agant l av- ,4

United States Patent PHOTOGRAPHIC 0R CINEMATOGRAPHIC HIGH-SPEED TELE-OBJECTIVE Rudolf Solisch, Gottingen, Germany, assignor to Isco Optische Werke G.m.b.H., Gottingen-Weende, Germany, a corporation of Germany Filed Nov. 13, 1958, Ser. No. 773,607

Claims priority, application Germany Nov. 27, 1957 2 Claims. (CI. 88-57) My present invention relates to photographic or cinematographic objective of large focal length, i.e. to socallcd tele-objectives, in which a multi-component lens group on the object side of a diaphragm space, i.e. on the side of the longer light rays, co-operates with a single lens component on the image side, or side of the shorter light rays.

In my co-pending application Ser. No. 770,439, filed October 29, 1958, now Patent No. 2,910,914, I have shown that it is possible to provide a tele-objective of this character'having an aperture ratio of 1:2.8 or higher while utilizing five lenses, three of them combined into a dispersive triplet, of which all except the last two are made of a glass whose refractive index for the yellow 11,, line of the spectrum is less than 160. An objective as described in my co-pending application compares favorably with more conventional optical systems of similar structure in which, for the attainment of a like aperture ratio, it was necessary to use more highly refractive and therefore relatively expensive glasses throughout.

The object of my instant invention is to realize a similar advantage in a tele-objective in which the number of lenses is reduced to four.

I have found, in accordance with this invention, that the teachings of my above-identified application are also applicable to an optical system in which the first two constituents of the aforementioned triplet are comlCC erably biconcave third lens exceed that of the biconvex second lens by a value ranging between substantially 0.12 and 0.18.

In accordance with still another feature of my invention, the sum total of the refractive indices n of all four lenses should be less than 6.80 while the sum total of their Abb numbers v should be below 175.0. Such a system, aside from being inexpensive to produce, affords a substantial elimination of particularly comatic aberrations and a satisfactory flattening of the field which, with a high-speed objective of aperture ratio 1:2.8, will have an extent of 114.

The invention will be described in greater detail with reference to the accompanying drawing in which Figs. 1 and 2 illustrate different embodiments corresponding to the two variants referred to above.

The tele-objective shown in' Fig. 1 comprises a front group, consisting of a collective singlet I and a dispersive doublet Ii, and a single rear component III. Singlet I is a meniscus-shaped, almost plane-convex positive lens L having radii of curvature r r and thickness d;; it is separated by an air space d from the doublet II consisting of lens elements L and L cemented together. Lens element L having radii r r, and thickness d;,, is of hiconvex configuration. Lens element L (radii r r and thickness d.) is biconcave and represents the only part of the front group which has an index of refraction greater than 1.60. Rear component III, separated from doublet II by a diaphragm space d is shown as a single planoconvex lens L having radii r r, and thickness d similarly to lens element L the singlet L also consists of a glass of relatively elevated index of refractivity exceeding 1.60.

The system shown in Fig. 1 may be designed for a relative aperture of 1:2.8 and a back-focal length of s'=42.8, based upon an overall focal length of numerical value 100. Representative numerical values for the parameters r to r, and d; to d of lenses L to L together with the refractive indices n and the Abb numbers v thereof, are as follows:

bined into a single biconvex lens. This biconvex lens, along with the collective singlet preceding it, is made in accordance with the present invention of a glass whose refractive index is less than 160.

I have also found, in accordance with a further feature of my invention, that the rear (image-side) surface of the biconvex lens may be either cemented onto the immediately following, dispersive third lens of the front group or may be separated therefrom by a small air space, the latter variant being optically equivalent to the former if the closely spaced, substantially concentric surfaces of these two lenses are treated in well-known manner to minimize reflexes at the glass/air interfaces. In either case it is desirable that the refractive index of the pref- Fig. 2 shows a modified system according to the invention, consisting of four air-spaced lenses L L L and L all of substantially the same configuration and refractive index as their counterparts in Fig. l. Singlet 1, consisting of front lens L has radii r r and thickness (1, and is nearly identical with singlet I in the preceding embodiment. The doublet II of that embodiment has been split into singlets Ila, IIb respectively consisting of the lens elements L (radii r r, and thickness d and L (radii r r and thickness d The two almost concentric adjoining surfaces r r of these lenses, which turn their concavities toward the object side of the system, are separated from each other by a gap :1, which is a fraction of the air space d, between lenses 3 L and L Rear component III, positioned beyond the diaphragm space d is represented by lens L having radii r r and thickness d Listed below are representative numerical values for 4 2. A tele-objective system consisting of three front lenses and a single rear lens, said front lenses consisting of a collective singlet followed by a dispersive lens pair composed of a biconvex forward element and a biconthe parameters r to r and 11; to d of the lenses L 5 cave rear element, said singlet and said forward element to L, of Fig. 2, again based upon an overall focal length having each an index of refraction less than 1.60 whereof numerical value 100, in a system having a relative in the numerical values of the radii of curvature r to r, aperture of 1:2.8 and a back-focal length of s'=42.2. of said singlet L said forward element 14 said rear Table B Thlcknesses Lens Radli and air m 1! Spaclngs n'=+ 72.91 I L1 d|'= 3.95 1.58913 01.2

da'=- 0.60 air space T3'=+ 36.09 Ila L d;'=22.40 l.58900 48.6

d(- 0.15 air space r 94.40 Ilb L1 d5= 8.70 1.72825 28.3

d =19. 35 diaphragm. space T;'=+ 57.34 III L. (11'= 4.30 1.67270 32.2

d......,=59.45 mn..1=6.5790s tatal=l7o.a

It will be seen that in both embodiments the refracelement L and said rear component L as well as the tivity of the rear clement L or L of the dispersive pair thicknesses and air spacings d to d-; thereof, based upon of the front group exceeds that of its mate L or L by a numerical value of 100 for the overall focal length a value ranging between the aforestated limits of 0.12 of the system, the refractive indices n of the elements and 0.18, this value being approximately 0.15 in the case L to L and the Abb numbers v thereof are substanof Table A and 0.14 in the case of Table B. The sum tially as given in the following table: totals of the refractive indices n and of the Abb numbers 1! lie in each case well below the limiting values of 6.80 and 175.0, respectively. Le R (n Thlcgirntlzsses I HS 8 I an ar '"d I s 1 v 1. An optical tele-objective system consisting of three [no front lenses and a single rear lens, said front lenses consisting of a collective singlet followed by a dispersive 40 l dl'=3.95 1. 53913 01.2 lens pair composed of a biconvex forward element and =+4m91 ago, air space a biconcave rear element, said singlet and said forward L, a'=+ H element having each an index of refraction less than I 1.60, said forward element and said rear element being I 4 ir pace cemented together, the numerical values of the radii of LES-25 2&3 curvature r to r, of said singlet L said forward element n=+ d M19 3, h r p l L said rear element L and said rear component L as ragnsme well as the thicknesses and air spacings d to d; thereof, 1.67270 312 based upon a numerical value of 100 for the overall focal length of the system, the refractive indices n of the elements L to L and the Abb numbers v thereof being substantially as given in the following table: References C ted in the file of this patent L R I g k i r UNITED STATES PATENTS ens M 11 8D 71 Spacings $360,667 Mlnor Nov. 30, 1920 ,l86,622 Bertele Jan. 9, 1940 n=+ 72.01 0 2,562,012 Bertele July 24, 1951 M 1-58913 2,721,501 Bertele on. 25, 1955 dz= 0.60 airspace 2,750,839 Schade June 19, 1956 mm so 2,780,138 Eismann er a1 Feb. 5, 1951 =-11B.95 r 23 20 d 8.65 1. 74077 27.7 FOREIGN PATENTS S n=+ Phrase-5pm 350.323 Great Britain June 11, 1931 d 4.30 1. 67270 3 2 4 =0 a 2' c6 

